Method and apparatus for controlling fuel beds



Jan. 11, 1938. H. s. MORTON 2,104,883

METHOD AND APPARATUS FOR CONTROLLING FUEL BEDS Filed April '7, 1934 5Sheets-Sheet 1 1938. H. s. MORTON I METHOD AND APPARATUS FOR CONTROLLINGFUEL BEDS Filed April 7, 1934 5 SheetS- -Sheei 2 Jan. 11, 1938. H. s.MORTON METHOD AND APPARATUS FOR CONTROLLING FUEL BEDS Filed April 7,1934 3 Sheets-Sheet 3 Patented Jan. 11, 1938 UNITED STAT ES P O F F ICEMETHOD AND -APP ARAT U S FOR CONTROL- LING FUEI'rBEDS Harold's.MortonIStE Paul, Minn.

Application'Aprii 7, 1934; Serial N0. 719,582

19 be conveniently measured in the fire itself, but

may be determined by any'suitable means for I determining its velocityof flow before it reaches thefire. I have found that if a Venturi tubeis placed in an air'duct through which air flows from a forced draftfanto the wind box of a stoker, that as long as the fuel'bed'remainsapproximately constant, the reduction in pressure at the throat of'theventuriis in direct proportion I to the pressure differentialcausingfiow of air 'th1011gh' the fuel bed, since both are directlyproportional to the square of the rate of air flow. When the thicknessof the fuel bed decreases slightly the velocity in the air ductincreases, thus providing a further reduction of pressure in the Venturithroat and throwing this pressure reduction out of the desiredproportion. As the fuel bed-approaches proper :depth, the velocitydecreases, raising the reduced pressure at the Venturi throat andrestoring the normal ratio between it and the pressure causing'flow.

Ina previous application; I regulated thefuel bed by'arbitrarilyproportioning the size of the air duct in which the Venturi tube wasplaced so that with a normal fuel bed condition the reduction inpressure at theVenturi throat-was equal to the'static' pressure in-theair duct. This resulted in exactly atmospheric pressure at the Venturithroat under normal fuel bed conditions, because the reduction inpressure due to the ve- 40 locity offlow is'subtracted from the staticpressure in;-the duct and the net result is zero pressure. This,however, often necessitated an extremely high velocity in the air ductto provide a negative pressure in the Venturi throat-large enoughtoequal'andbalance the positive static pressure; and'it resulted in lossof pressure and capacity in the air duct so that larger fans'and morepower were needed to deliver the required quantity of air to the fire atthe required pressure.

It is therefore the object of this invention to avoid the necessity forsuch high velocities and such wastefullosses of air pressure and ductcapacity, by eifecting properfuel-bed control when the reductionin'pressure; at'rthe Venturi caused by the venturi, so that any inequality;between the two acts ,to change the rate of fuel 'vide'a conduittransmitting air duct pressureto 'nected'toatmosphereor"'preferably tothe com "bustion chamber abovethe'fireS'By' adjusting the throat is {notequal to'the static pressure, but

.is some: lesser amount' whi'ch can be realized =with mo're liberal ductdimensions and lower air velocity. Thisreduction inpressure is,proportional, under any desired fuel bed conditions, to" 5 the pressurecausing flow of air through the fire,

'and Iutilize this proportionality in-thisinvention, rather than theequality of pressures which was necessaryin my previous invention. Itis, thereforey-the purposegof'this invention 'to pro-- vide a balancebetween the reduction in pressure at the Venturi throat caused by airvelocity; and

some proportional part or-fraction of'the total {pressure differentialacting on the fuel bed.

In providing a balance between pressure'dif 15 ferentials, various typesof apparatus could be used. Inverted bells of unequalareas might bebalanced against one another. Bells, or -diaphragms 'ofunequal areamight similarly be balanced against one another. Bells or diaphragmscould be balanced against one another by-linkages'having a propermechanical advantage to compensate for the ratio of the two magnitudesof pressure differentials. 'Ihe resultmay also be accomplished byreducing the difierential of 12 highermagnitude in some definite ratiountil it a is on a par with the one of lessermagnitude so that a directbalance between the two becomes feed in a way which'will bring the fuelbed back to normal and restore the balance betweenthese pressuredifierentials.

In carrying out myinvention', I preferably pros a pressure reductionchamber. orifices, adjustable' in size, control the "inlet to'thischamber from the conduit, and the'exhaust, which is'c'onair'ductminusthe drop through the inlet orifice. *The pressureatthe'venturithroat-is at-a-pres-w Y sure equal to the'static pressure in the airduct minus the reduction due to velocity at the Venturi throat. Sincethe two pressure differentials which I wish to balance against eachother are each subtracted from the same pressure (viz. the staticpressure in the air duct) it is possibleto balance the pressure at theVenturi throat directly against the pressure in the chamber between theinlet and exhaust orifices described above, knowing that whenever thereis an inequality between the two pressure differentials, there will be alike inequality between the differences resulting from the subtractionof two unequal pressure drops from a common initial pressure. Bychanging the relative sizes of the orifices, any desired proportion ofthe total pressure drop acting on the fire may be made to take placethrough the inlet orifice, and thus it is possible to arbitrarilycontrol the fuel bed thickness at which the Venturi reduction willbalance the drop through the inlet orifice. The control tends tocontinually maintain whatever fuel bed condition is predetermined whenthe relative size of the orifices is adjusted to any desired value.

In balancing the pressures as above outlined, it is possible for me toutilize a sealed bell or diaphragm which balances the pressure betweenthe Venturi throat and a desired adjustable proportion of the pressureused in forcing air through the fire. When the velocity in the air ductbecomes too great or too small in relation to the pressure causing flowof air to properly balance the adjusted diaphragm or bell, the bell ordiaphragm moves, acting to close an electric switch connected therewith,for turning on or off the stoker motor.

It is also a purpose of my invention to provide a means for delaying orretarding the movement of the switch or operating means therefor. Bythis means it is possible to require a substantial difference inpressure between opposite sides of the diaphragm or bell before theswitch will open, while the switch will close as soon as the pressure onone side of the bell or diaphragm drops below that of the other side, orvice versa. By this adjustment it is possible to maintain a perfectcontrol of thefuel bed for every draft condition, without too frequentstartingand stopping of the fuel bed.

I further provide a means of controlling the stoker motor or fuelfeeding means which is sensitive enough so that even the natural draft,which draws air through the fan, duct, and fuel bed when the fan is notoperating, will cause the control to operate and add fuel as needed tokeep the fire from burning down too low.

The drawings disclose the apparatus which I employ to carry out themethod herein by reducing the differential of higher magnitude by adefinite ratio until it is on a par with one of lesser magnitude so thata direct balance between the two is obtained, to provide a sensitive,inexpensive controller for a stoker.

Figure 1 diagrammatically illustrates a portion of a fire box andstoker, showing the means and apparatus of carrying out my method.

Figure 2 is an enlarged plan view of a portion of the apparatus.

Figure 3 is an enlarged sectional side view of the apparatus illustratedin Figure 2. I Figure 4 is an outer side elevation of the apparatusillustrated in Figure 3.

Figure 5 illustrates another form of the apparatus in side sectionalelevation, showing a difierent connection of the air pipes to the bellchamber and a different valve control.

Figure 6 is a plan View of a diaphragm control which may be used inplace of the bell.

Figure '7 is a sectional view through the diaphragm control illustratedin Figure 6.

The furnace A illustrated in the drawings is adapted to be fed by astoker feeding screw or plunger B to feed fuel 10 onto the grate or deadplate C to maintain the desired fire in the furnace A.

An air fan D provides the draft of air to the grate C through thechamber H through the air conduit [2 leading from the fan D to thechamber H.

In carrying out my method I provide a controller E which is adapted tobe regulated by the adjustable valve l3. The valve I3 is set into thedesired position by the hand lever l4 and the indicating pointer carriedby the handle [4 indicates the position of the setting of the valve. Inconjunction with the pointer I5 I provide indicia is which may indicatea steady fire at the central setting of the valve and to one side ofthis central setting the indicia of Heavy and run is indicated, and tothe other side Light and stop. Thus when the handle [4 is set to set thevalve I3 toward Heavy the fire and fuel bed IE] will be heavier thanwhen the handle I4 is set with the pointer toward Light which indicatesa lighter or thinner fuel bed.

The controller E in its preferred form may be provided with an invertedbell H, the inner portion of which is connected by the tube [8 to thepipe l9 which extends out through the bottom of the controller E andwhich is connected to the venturi 20 located within the air duct l2leading from the fan D to the air chamber II.

The bell I! is adapted to be balanced on the pivot point 2| whichsupports the lever 22 which is pivotally connected to the member 23extending from the top of the bell Ill. The lever 22 is adjustablyconnected to the counter-balance weight 25 through the channel orU-shaped member 25 which is pivotally connected at 2'6 to the rod 21extending from one end of the lever 22. The rod 2! is adjustablyconnected by the lock nuts 28 to the end of the lever 22 so as to setthe member 25 in the desired position in relation to the end of thelever 22. The member 25 straddles the outer end of the rod 21 and isadjustable in relation to the same on its pivot 26 by means of the setscrew 29 so as to raise or lower the center of gravity of the weight 24in relation to the pivot point 2: of the lever 22. By this means i thebell i! may be adjustably counter-balanced in the bell chamber 30. Theupper end 3! of the bell chamber is connected by the cam valve 3 to theports and 33. The port 32 is connected by the pipe 34 to the air duct I2as diagrammatically illustrated in Figure 1, while the port 33 isconnected by the pipe 35 to the fire chamber 36 of the furnace A.

The bell I! is adapted to support a mercury electric switch 37 which isconnected by the wires 38 to the terminals 39 which extend into thecornpartment fill inclosed .by the casing ti on the side of thecontroller E. Suitable electric conductors, not shown, lead out from thecasing ll and from the terminals 39 to an electric motor which isadapted to operate the screw or plunger fuel feeding means B, the motornot being illustrated in the drawings, however, the feeding screw Bbeing illustrated in Figure 1.

The mercury switch 3? is set to operate when the'bell I1 is down in theposition illustrated in Figure 3 or 5, so as to complete a circuit tooperate'the motor to feed fuel to the fuel bed In through the operationof the'screw B. When enough: fuel has been fed in to cause an increasein fuel bed resistance and a decrease in air flow, the excess ofpressurebelow will raise the bell l1, causing the switch 31 to turn offthe circuit to the motor which operates the screw B, and should theratio become unbalanced from the predetermined requirement to maintainthe fire or fuel bed l at the'desired depth, the bell I! will lower toop erate the switch 31. In this manner the fuel bed Ill may bemaintainedas desired in the furnace A. The valve I3 is set by the handleI4 to adjust the ratio of airpressure between the air pressure from theVenturi 20 to one side of the bell, and the connection 34 through thevalve I3 to the other side of the bell, to give the desired balancethrough the controller E. By operating the lever l4 with the arrowtowardthe indicia Heavy, the duct 32 will be opened wider owing to themounting of the valve l3 off-center, whereas, the duct 33 will be closedin proportion to the opening of the duct 32, thereby changing the ratiobetween that indicated through the venturi to one side of the bell, andthat indicated by the connection 34 to the other side of the bell. Itwill be apparent that when the controller E is set that any change ofthe fuel bed ID to permit more or less air to pass through the same fromthe duct 12 will change the air velocity and pressure in the duct l2,throwing the controller E out of balance and causing the switch 31 to beoperated. In this manner I control the stoker B and maintain the fuelbed IE as desired.

With the adjustment of the balancing means of the lever 22 of the bellI! through the adjusting screw 29 to change the center of gravity of theweight 24 in relation to the pivot 2|, I am able to retard the movementof the switch 3'! in a manner so that the control will not operate attoo short intervals or fluctuate back'and forth rapidly between the onand off positions. While I have illustrated a means of adjusting thebell ll, any suitable means of balancing the same and adjusting thebalancing means to retard the bell through a certain period may beemployed. The valve I3 is adjustable to regulate a pressure reductionthrough the connection 34 from the duct [2 and the connection 35 fromthe valve to the fire chamber 36 to set the controller E for the desiredratio of operation. With this means I am able to secure a better methodof controlling a stoker and the fuel bed thereof where I provide abalance by the proportional pressure differentials rather than by myformer method where equal pressures were desired to be maintained tooperate the controlling means. This method is more inexpensive to carryout and maintain.

In Figure 5 I have illustrated the controller E connected in a difierentmanner than that I have just described. In this figure of the drawings Ihave shown the controller E with the Venturi pipe l9 connected at thetop into the bell chamber 3|, whereas, the pipe I8 leading inside of thebell I7 is connected through the adjustable valve 40 to the pipe 34which leads to the air duct l2 and through the adjustable valve 4| tothe pipe 35 which leads to the fire chamber 36 of the furnace A. Thevalves 40 and 4| operate in a similar manner as the valve l3 to balancethe pressure in the controller E, excepting that they are each separatevalves, thus providing means to obtain the desired pressure reduction tobalance the pres- 'sure from the Venturi with that from the duct throughthe connection 34. It will be apparent that the same result may beobtained as heretofore set forth in the description of the structureillustrated in Figure 3 with the connections as illustrated in Figure 3,excepting that the connections are reversed in Figure 5 to show that thebalance ratio may be carried on through the controller E in a reversemanner. The controller E is of the same structure, but the connectionsinto the belland above the same are reversed.

In Figures 6 and '7 I have illustrated a diaphragm controller F which isprovided with a diaphragm 42 having a chamber 43 which is connected bythe pipe H! to the Venturi 20, while the valves 44 and 45 are connectedby the pipes 34 and 35 to the air duct l2 and the fire chamber 36,respectively. The valves 44 and 45 are con nected through the chamber 46and the passageway 41 to the chamber 48 on the opposite side of thediaphragm 42 to the chamber 43. Within the chamber 43 I provide asuitable el'e'ctric switch 49 which is connected to the diaphragm and tothe casing so that in the movement of the diaphragm the switch 49 isopened or closed. The central position of the diaphragm 42 illustratedin Figure 7, shows the switch 49 with its terminals open so that thecircuit operated by the same would be open when the diaphragm 42 is inthe position illustrated. Suitable electrical conductors, not shown,lead from the switch 49 to operate the motor of the stoker B. The valves44 and 45 are of the same nature as the valves 40 and 4| and may beoperated in the same manner to provide a pressure reduction means in thecontroller F.

With my method a stoker for a furnace may be regulated to maintain athin fuel bed on the grate for a certain type of fire or may beproportionately increased to maintain a heavier fuel bed, the primaryobject being in the method of controlling the fuel bed.

The method of controlling a stoker has been defined as using acontroller such as E or F which are only illustrative of a means ofcarrying out the method. It is apparent that the method comprisescontrolling the fuel bed by means of the resistance of the air throughthe same, whereby any variations in the air velocity or static pressurein the draft duct to the grate or in the relationship between the twomay be utilized to operate an electric switch or other suitable means tocontrol the feeding of fuel to the fuel bed. It is also apparent thatthe method may be employed for operating any component part of a stokerso as to completely control the same.

Thus I have provided a simple method wherein the balance betweenproportional pressure differentials between the velocity and static inthe air duct connected with the combustion chamber of the furnace may beutilized to give a more desirable means of controlling a stoker tomaintain a predetermined fuel bed and fire in the furnace.

I claim:

1. A static operated controller including, a housing, a pressure bell,adjustable means for balancing said bell within said housing, an airpassage connecting the draft duct of the furnace with the combustionchamber thereof, a pressure reducing valve interposed in said airpassage, a venturi positioned in the draft duct of the furnace connectedunder said bell, said valve in said controller operating to balance thereduced air pressure between the draft duct and the, combustion chamberin relation to the velocity pressure from the venturi to provide apredetermined setting for said controller, and an electric switchcarried by said bell and adapted to be operated by the unbalancing ofthe bell by a change in the static pressure or velocity in the draftduct or the combustion chamber of the furnace which unbalances saidcontroller.

2. An air operated controller for stokers and the like including, apressure chamber, a member operated from said pressure chamber, anelectric switch carried by said member, an air balancing chamber on theopposite side of said member to said pressure chamber, a venturi, meansfor connecting saidventuri to said first pressure chamber, means forconnecting one side of said balancing chamber to the air duct in whichsaid venturi ispos'itioned, means connecting the other side of saidbalancing chamber with the fire chamber of a furnace, adjustable valvemeans in said balancing chamber for setting said air operated controllerto a predetermined balancing position between the velocity and staticpressure in the draft duct as relating to the pressure in the firechamber, whereby when the ratio between the air duct and the firechamber changes from the setting of the air controller, said electricswitch will be operated to control the fuel bed regulated by the stoker.

HAROLD S. MORTON.

